Matched potential control system



Feb. 27, 1951 G. DEAKIN MATCHED POTENTIAL CONTROL SYSTEM Filed July 16, 1945 the register switch which responds to the `digit to be matched by the illustrated selector. When brush RB is advanced toward one of its ten terminals in accordance with the operation of the calling device at station I, the relay ARI having been energized in the customary manner, a circuit is closed from ground over the back armature and its front contact of relay ARI, the armature and back contact of register relay VR, the winding of selector relay AR and the magnet P to grounded battery. Magnet P is energized, and the brushes of selector switches 3 are driven over the selector` terminals ST continuously in known manner until relay VR is energized and breaks the circuit of magnet P. The circuit of relay VR extends from the anode of tube V through the back contact and armature of relay PCR, the winding of relay VR and the front armature and front contact of relay AR] to grounded high tension battery HTB. The winding of relay VR may be shunted by resistor R5 if necessary to obtain the desired operation.

Each of the register terminals RT is connected through a suitable resistor to a source of potential, and the selector terminals ST are similarly connected, the potentials of successive terminals advantageously varying progressively by the same amount, which in the illustrated embodiment is four volts, though it will be understood that this particular potential arrangement may be varied within the scope of the invention.

The register brush RB is connected to the cathode of tube V and the selector brush T is connected to the control grid of the tube, preferably through a biasing resistor R2. Brush T is advantageously connected through a high value resistor R4 to the negative terminal of grounded battery B, in order to prevent false operation when the brush T is not in contact with a terminal ST.

Brush T is connected through the Winding of relay PCR to brush RB, while the armature and back contact of the relay are in the circuit from the anode of tube V through the winding of relay VR. With this arrangement, whenever the potential difference between the brushes RB and T is sufcient to energize relay PCR, the anode circuit will be opened and relay VR cannot be energized to open the magnet circuit and arrest the selector brushes. brushes will be stopped only when the potential difference between brushes T and RB is insuflicient to energize relay PCR. In the disclosed arrangement this will occur when these brushes are at substantially the same potential. It is noted that the negative control grid bias necessary for obtaining adequate anode current in certain types of tubes when the brushes are at the same potential may be provided independently of the potential applied to relay PCR, as by the use of the biasing resistor R2.

In order to prevent relay PCR from operating uselessly to open the anode circuit when the control grid is below cut-off potential a blocking rectier S is advantageously inserted in the circuit of relay PCR, arranged to prevent material current flow through said circuit when the polarity of the brushes is appropriate to produce said cut-oil potential.

It is desirable to reduce to a minimum value consistent with good operation the current flowing through relay PCR. Excessive current now may occur when the potential difference between the brushes T and RB is greater than a safe operating value, and is likely to result in overheat- Consequently the selector ing and sparking dilculties at the terminals. Where other circuits have portions which lie parallel and adjacent to the lines carrying such excessive current, cross talk is also likely to take place, and specifically the production of clicking noises in the other circuits. The invention therefore includes an arrangement for preventing excessive current ow through the lines connecting the brushes, regardless of the potential difference between the brushes.

For this purpose a relay PCRI is advantageously connected in series with relay PCR, and is arranged to cut into circuit with the winding of relay PCR a resistance which will reduce the current through the latter relay to a substantially lower value consistent with holding the armature in front position. The resistance is advantageously in series with the windings of the two relays and is shunted by a circuit through the armature and back contact of relay PCRI so that the resistance will not be cut into the circuit until the relays have operated.

A convenient arrangement of this type is illustrated and utilizes the reactance of the winding of relay PCRI as the resistance, the armature of relay PCRI being connected to one end of the winding and its back contact to a tap on the winding near the other end, providing a shunt for the major portion of the winding when the relay is deenergized. In one effective arrangement the shunted portion of the winding has a reactance of 5,000 ohms while the unshunted portion has a reactance of ohms. It was found that with a relay PCR having a reactance 1,000 ohms the initial current was suflicient to energize relay PCR, opening the shunt across part of the winding PCRI, and that the resultant reduced current was sunicient to hold the armature of relay PCR in front position.

The desired results will be obtained when relay PCRI is designed to operate at the same DO- tential as relay PCR; but since the current will have a proportional relationship to the potential difference between brushes T and RB, diiculties with excessive current are more likely to occur when the potential difference is substantially above the minimum. Relay PCRI may therefore be of a type which will not operate at such minimum potential difference between the brushes, but will be energized at a higher potential diierence, so that the series resistance is shown in only when the current threatens to become excessively great. For instance, relay PCR may operate at the minimum potential difference, even when relay PCRI and rectifier S are connected in series, the illustrated example disclosing a minimum difference of four volts; while under the same conditions relay PCRI may require a potential of over ten volts, so that it will not trip unless the difference between the brushes is equal to at least three successive voltage steps.

Relays PCR and VR are selected so that the former will open first, preventing inadvertent energizing of relay VR and the resultant opening of the circuit through magnet P before relay PCR can operate to cut out relay VR when brushes T and RB are on unmatched terminals.

It will be understood that the invention has been illustrated without complicating it by the inclusion of other parts of the automatic telephone system in which it may be used, an embodiment of which is illustrated in the abovementioned Deakin application. Certain features which might be added to adapt the illustrated arrangement to particular uses, to produce particular types of operation or to adapt the circuit to tubes having different characteristics have likewise been omitted, since the use of such features under appropriate conditions will be apparent to those skilled in the art.

Moreover, While the illustrated. embodiment is especially adapted for use in automatic telephone systems, and in particular the relay system actuated by the anode current of the tube is or a type suitable for use in Such Systems, it will be apparent that other types of controlled devices may be actuated by the anode current. Likewise, diierent arrangements for selecting and applying the potentials to the two sides of the switching system may be employed, though the disclosed arrangement has particular advantage when used with automatic telephone systems including a selector and register, or corresponding arrangements.

What is claimed is:

1. In a telecommunication system, a selector switch comprising a plurality of terminals at dierent potentials, a brush and means for moving the brush over the terminals; switch comprising a plurality of terminals at different potentials and an associated brush; and means for arresting the selector brush when the brushes have a predetermined potential relationship, comprising an arresting relay and means for reducing the current thro-ugh the arrestingr relay while maintaining the relay in operation, including a regulating relay having a Winding in series with the arresting relay Winding, a resistance in series with said windings and a circuit including the armature and baci: contact of said regulating relay shunted across said resistance, arranged to place said resistance in circuit with said arresting relay Winding only after said regulating relay is operated.

2. An a 1'rangement as set forth in claim 1 in which the resistance comprises a portion of the winding cf the regulating relay.

3. An arrangement as set forth in claim l in which the minimum operating potential of the regulating relay is substantially higher than the minimum operating potential of the arresting relay.

4. An electric control system comprising actuating means including a device responsive to current flow and means for reducing the now of said current after the device is actuated, including a relay having a winding through which the current passes, an impedance in series With the Winding and an armature and back contact connected in shunt with the impedance, arranged to short circuit the impedance until said device and relay are energized by current iioW, and to cut in the impedance and reduce the current flow when the relay is energized.

5. A system as set forth in claim 4 in which the impedance is part of the winding of the relay.

6. A system as set forth in claim 4 in which the responsive device includes a relay having a Winding in series with the Winding of the current reducing relay.

a register y 7. In a telecommunication system, a selector switch comp g a plurality of terminals at different pote a brush movable over said terminals, and means for arresting the movement of said brush comprising an arresting relay and a regulating relay, the latter having a Winding in series with the vEor ier, and operable only at a potential which is sus tantially higher than the minimum operating potential of said arresting relay.

3. In telecommunication system, a selector switch comprising a plurality of 'terminals at different potentials, a brush ovable over said terminals, and means or arre ting the movement of said brush comprising an arresting relay, means for operating .said arresting relay, and means iorreducing the current lovv through said relay While maintaining it in operation.

9. in a telecommunication system, a selector switch comprising a plurality or terminals at different potentials, a brush, and means for moving the brush over the terminals; a register switch compi'sing a plurality of terminals of different potentials and an associated brush; and means for arresting the movement of the selector brush when the brushes have predetermined potential relationship comprising a vacuum tube having at least 'three electrodes and operative when a iirst electrode is above a cut-oil potential relative to a .second electrode, means actuated by said tube for arresting the movement of the selector brush, means connecting each brush to a diiierent one of said first and second electrodes, and means including a relay connected across the brushes for disconnecting the tube from the arresting means when the first electrode is not less than a predetermined potential higher than the cut-oil potential.

10. 1n a telecommunication system, the combination, according to claim 9, in which the disconnecting means further includes a blocking rectifier in series with the relay Winding, arranged to prevent current flow through said winding when the rst electrode is at cut-oli potential.

GERALD DEAKIN.

REFERENCES CITED The following references are of record in the ille of this patent:

rUNITED STATES PATENTS Number Name Date 137,730 Smith Apr. 8, 1873 1,621,011 Harvey Mar. 15, 1927 2,008,563 Sarbey July 16, 1935 2,061,011 Vingerhoets Nov. 17, 1936 2,070,900 Harris Feb. 16, 1937 2,158,261 Urtel et al. May 16, 1939 2,312,357 Odduist et al Mar. 2, 1943 2,341,919 Hubbard Feb. 15, 1944 2,354,667 Deakin Aug. 1, 1944 2,376,346 Deakin May 22, 1945 2,380,950 Deakin Aug. 7, 1945 2,419,548 Grieg Apr. 29, 1947 2,428,024 Herbig Sept. 30, 1947 

